1. Field of the Invention
The present invention generally relates to a method and apparatus for measuring timing characteristics of low to moderate rate bursty message traffic over a digital transport. xe2x80x9cBurstyxe2x80x9d is a term used to describe information that flows unevenly, intermittently or asynchronously, with intense periods of activity followed by relatively long, silent intervals typically of varying length.
2. Background Description
Various methods and apparatuses have been used for measuring pulse streams over various transports. These include logic analyzers of different kinds and microprocessor-based test devices. Logic analyzers are very expensive. Since they are relative complex, general purpose devices, significant work and expertise is needed to conduct timing tests using a logic analyzer. Furthermore, captured data may not be in a format conducive to further analysis using common personal computers. Microprocessor-based devices are also very expensive and, in some cases, lack facilities for transferring captured data to a personal computer for further analysis.
In an unrelated technology, the specifications for the Musical Instrument Digital Interface, or MIDI for short, were established in the time period between 1981 and 1983 by a group of electronic musical instrument manufacturers. Since that time, the specification has been augmented from time to time. Basically, MIDI is a software and hardware specification by which musical data is transferred among hardware devices, allowing keyboards to xe2x80x9ctalkxe2x80x9d to computers, synthesizers and other digital music devices. The source of the MIDI standard is xe2x80x9cThe Complete MIDI 1.0 Detailed Specificationxe2x80x9d, Version 96.1, MIDI Manufacturers Association, March 1996.
Since a MIDI data stream is a serial data stream, a personal computer can receive the data, note the time the data was received and then store both these quantities into memory or onto disk. This data can be manipulated by suitable software, and the computer can play back the data to a synthesizer via a MIDI connection. This type of program is called a sequencer.
It is therefore an object of the present invention to provide an inexpensive solution to the problem of measuring timing characteristics of message-oriented transports, using common personal computers which easily support a wide variety of analytical tools.
It is another object of the invention to provide a way of measuring timing characteristics of message-oriented transports that requires little expertise to conduct tests.
It is a further object of the invention to measure timing errors resulting from less than perfect transmission of low-speed MIDI data over high-speed transports.
According to the invention, there is provided a means of accurately measuring timing characteristics of bursty message traffic over relatively low to moderate rate digital transports such as the Musical Instrument Digital Interface (MIDI). The apparatus includes means for generating a reference pulse stream, such as a sequencer. A transcoder device receives the reference pulse stream and routs the pulse stream to a device under test and, in analog form, to a first channel input of a digital recording device, such as a sound card installed in a personal computer. The transcoder also receives an output pulse stream from the device under test and routes the output pulse stream, in analog form, to a second channel input of the digital recording device. The invention provides the following advantages:
Low hardware cost,
Highly accurate timing measurements,
Differential technique that allows timing errors in the reference pulse stream to be eliminated from measurements, and
Easily supports a broad variety of analysis techniques using common software on personal computers.